Process for the removal of hydrogen halide from halogenated compounds



Patented Apr. 12, 1949 UNITED srArEs PATENT OFFICE I raoosss Fort rn a ziffovan F HYDRO- GEN HALIDE FROM HALOGENATED COM- POUNDS Elmer E. Fleck,Silver SpringyMd and Herbert L. J. Heller, Washington, D. 0., assignorsto United States of America as represented by the Secretary ofAgriculture No Drawing. Application May 18, 1944, Serial No. 536.226

2 Claims. (Cl. 260-649) (Granted under the act of March 3, 1883, asamended April 30, 1928; 370 0. G. 757) This application is made underthe act of March 3, 883, as amended by the act of April 30, 1928, andthe invention herein described, it patented, may be manufactured andused by or for the Government of the United States of America forgovernmental purposes without the payment tons of any royalty thereon.

This invention relates to a process for the catalytic removal ofhydrogen halides from halogenated aliphatic hydrocarbons and from theside chains of araliphatic hydrocarbons containing halogen substituentsin the aliphatic side chains.

The dehydrohalogenatlon of organic compounds by means of alkali is awell known general reaction which has been applied in splittin hydrogenhalide from a wide variety of halogenated organic compounds to producenumerous unsaturated organic compounds. The reaction has been applied inmaking ethylene from ethyl bromide, l-chloropropylene from propylidenechloride, allylene from l-bromopropylene, cyclohexane from cyclohexylchloride, and so forth.

A common characteristic of the organic reactants for such reactions isthat they each contain in a non-aromatic (i.e., an aliphatic oralicyclic) portion'of the molecule the radical instead of the much lessvaluable halide salt. The reaction may be carried out without the use ofa solvent, although it is preferable that the halogenated compound be inthe liquid state when in contact with the catalyst. The reaction mayalso be carried out with the halogenated compound in the gaseous state,or with the halogenated compound dissolved in an inert hydrocarbonsolvent, nitrobenzene, chlorinated benzene, cyclohexanone and otherketones.

The temperature at which the reaction may -be hydrohalogenation to takeplace. The relative effectiveness of some of these catalysts is shown inthe table.

Table [2 g. p-dichlorodiphcnyltrichlorethane 2 2. catalyst heated forone hour at 115 120 0.]

III 11 80 Catalyst ggg gg wherein X represents halogen. I The reactionhas usually been carried out by iiiiiit yfiffi)?&&.Ftiifitfifigii:::::::::::: heating the organic reactant with a solution of ifgKOH in ethanol. Other caustics such as NaOH i c1,,%',ofj- 5.3 and othersolvents such as water and polyhydric g 6131) (Month 34 alcohols havebeen used. In these reactions the rymi'liia'iaj'sifiifi'e'i" 11ohydrogen halide reacts with the caustic to form v g A ri; sampler saltswhich must be removedfrom the reaction Talc(oli o16r3IIIIII 110 mass.Likewise, it is necessary to separate the de- 40 gg g 'f fg -g sireddehydrohalogenated compound from the olin 1Z0 solvents used. gg g 8-; Wehave now discovered that ferric chloride,011011.111IIIIIIIIIIIIIIIiIIIIIIIIIIIIIIIIIIIZIIIII 011 preferablyanhydrous ferric chloride, and certain other catalysts will cause thehydrogen halide to The catalyst may be used alone or supportedseparate-from .the halogenated compound whenheated under anhydrousconditions leaving the unsaturated compound in a relatively purecondition. When the unsaturated compound has a relatively high boilingpoint, the hydrogen halide, may be driven off as a gas; otherwise, itmay be removed by absorption in water or some other suitable solvent.The reaction proceeds without the aid of a caustic and results in theformation of dry hydrogen halide as a valuable by-product on a carriersuch as silica, alumina, and so forth.

The amount of catalyst may range within wide limits. For example, 0.05percent of anhydrous ferric chloride will remove 1 mol. of hydrochloricacid from p-dichlorodiphenyltrichlorethane in the course of 15 minutesat ll5-1 20 C. If 5 percent of the catalyst is used, the reaction is 1completed with the melting of the p-dichlorodi- 3 Our invention isillustrated by the following examples:

Example I The catalyst is prepared by placing 0.1 g. of fine ironfilings or iron powder in a 250 cc. Erlenmeyer flask. A slow current ofCl: is passed over the iron and the bottom 01 the flask is warmed with afree flame until sparking occurs. The flask is cooled and then freed'ofexcess chlorine with a current of dry air. Thep-dlchlorodiphenyltrlchlorethane (100 g.) is added and an outlet for theHCl gas is fitted to the flask and connected to an HCl absorber. Theflask is then heated in an oil bath maintained at a temperature between1l5-120 C. Gas evolution takes place as soon as the material melts andthe reaction is completed in about 30 minutes.

The product remaining in the flask is p-dichlorodiphenyldiohlorethylene,and the yield is quantitative. This product may be separated from thecatalyst by filtration while hot.

Example II The catalyst was'prepared as in Example I, and 100 g. of2,2-diphenyl-1,1,1-trichlorethane was heated with 0.1 g. of the catalystas outlined in Example I. A quantitative yield of2,2-diphenyl-l,1-dichlorethylene was obtained.

Example III 100 g. of 2-p-chloro-2-phenyl-1,1,1-trichlorethane wasreacted as described in Example I. A quantitative yield of2-p-'chloro-2-phenyl- ,1- dichlorethylene was obtained. 7

Example I V A mixture of 2 g. of p-dichlorcdiphenyltrichlorethane and -2g. of anhydrous ferric bromide was placed in a glass U-tube and heatedas in Example IV; The aqueous solution in the absorber was then titratedand it required cc. oi N/10 sodium hydroxide to neutralize the acidpresent.

Example VI The procedure of Example V was repeated with 0.1 g. ofcatalyst and 2 g. oi alpha,beta-dibromostyrene at a temperature of100-105. cc. of N/ 10 sodium hydroxide was required to neutralize theHBr collected in the water absorber.

Example VIII Example VI was repeated using alpha, betadichlorostyrene.After heating for one hour, 64 cc. of N/ 10 sodium hydroxide wasrequired to neutralize the HCl given off.

Having thus described our invention, we claim:

A process of removing hydrogen halide from the molecule of halogenatedhydrocarbons selected from the group consisting of halogenated aliphatichydrocarbons and araliphatic hydrocarbons containing halogensubstituents in the aliphatic side chains, which comprise heating in theliquid state under anhydrous conditions the halogenated hydrocarbon witha catalytic amount of anhydrous ferric chloride.

2. The process of claim 1 wherein the halogenated hydrocarbon isp-dichlorodiphenyltrichlorethane.

' ELMER'E. FLECK.

HERBERT L. J. HALLER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,084,937 Britton et a1 June 22,1937 2,134,102 Cass Oct. 25, 1938 FOREIGN PATENTS Number Country Date559,737 Germany Sept. 23, 1932 OTHER REFERENCES Thomas: AnhydrousAluminum Chloride in Organic Chemistry," pages 779-80, 867-8.

Brand et 2.1.: "Ber. der. deut. Chem. Gesell, vol. 72, page 1032 (1939).

